“Good morning, everybody. I have a major announcement today. We had our bodies measured after reaching space, and wow, wow, wow, I had actually grown by as much as 9cm!” he tweeted, adding “I grew like some plant in just three weeks. Nothing like this since high school. I’m a bit worried whether I’ll fit in the Soyuz seat when I go back.”

The Soyuz spacecraft is the one that takes astronauts from Earth to the ISS and vice versa, and their seats have a height limit.

However, his claim was incorrect.

Just hours later, he tweeted that Russian astronaut Anton Shkaplerov, commander of the mission, had been skeptical of the supposed growth, so the Japanese man measured himself again.

“It measured 182 centimeters, only two centimeters more than my size on Earth,” he wrote. “So it was a measurement error, but it seems that a lot of people are talking about it. I’m very sorry to have tweeted this false news.”

It is well known that astronauts grow in space, but on average it’s limited to just two and five centimeters. That increase is due to the absence of gravity, which causes the vertebrae to separate and the spine to expand. Once they return to Earth, the astronauts recover their original height.

This is the first space mission for Kanai, who was previously a Diving Medical Officer in the Japan Maritime Self-Defense Force.